Embodiments presented herein relate generally to aerodynamic surfaces configured for noise reduction, and more specifically to configuration of a tip portion on an aerodynamic surface, such as an airfoil, for noise reduction.
At least some known machines including aerodynamic surfaces such as, but not limited to, wind turbines, aircraft airframes, aircraft engines, gas turbine engines and steam turbine engines, include a plurality of stationary and/or rotating airfoils which are subject to impinging wakes and vortices generated from an upstream object, such as an upstream bladerow or an input unsteady airflow. The upstream generated wakes and vortices are channeled downstream where they may impinge on the leading edge of downstream airfoils. In one instance, the wake flow impingement, from an upstream object, on the downstream airfoils moving relative to each other is a dominant source of aerodynamic noise and aeromechanical loading generated in turbomachinery applications.
Of particular interest are unducted, contra-rotating engines which have been developed such as the GE 36 engine, frequently referred to as an unducted fan (UDF) or propfan engine. In some known unducted contra-rotating engines, noise may be generated by an upstream rotating airfoil's wake impinging on a leading edge of a contra-rotating airfoil located downstream. In other known instances, noise may be generated by an upstream stator component's wake impinging on a leading edge of a rotating airfoil downstream from the component.
Noise generated by aircraft engines may be constrained by international and local regulations, thereby creating a need to balance fuel efficiency and emissions with noise pollution. A dominant source of aerodynamic noise and aeromechanical loading generated in turbomachinery applications is the interaction of wakes from upstream bladerows on downstream bladerows or vanes moving relative to each other. As previously indicated, examples include fan wakes and vortices interacting with downstream contra-rotating fan blades, whereby open rotor noise may be generated by the forward-aft rotor interaction. In addition, of interest is turbomachinery noise from stator vane wakes impinging on downstream rotor blades. The impinging wake flow on the airfoil's leading edge may result in an increase in noise radiated from the turbomachinery, as well as a potential increase in aeromechanical loading on the bladerow. At least some known methods of reducing the noise generated by these unsteady wake flows impinging on airfoils include increasing the distance between the upstream object or airfoil and the downstream airfoil. This increased distance mixes the wake flow and thus reduces the amplitude of the wake flow forcing unsteady motion of the tip vortex of the downstream airfoil. However, increasing the distance between an upstream object, such as another airfoil, and the downstream airfoil may increases the size, weight, and cost of the engine, and thereby reduce the efficiency and performance of the engine.